The present invention relates to a method and a device for detecting and/or correcting misalignment of a distance sensor on a vehicle.
Some methods and devices for recognizing misalignment have been known to have the function of being able to self-correct their sensor viewing zone.
German Published Patent Application No. 197 46 524 describes a compensation device for compensating for the installation tolerances of a distance sensor in a vehicle. This is done by having the evaluation electronics registering the object distances and the object angles of the detected objects. These data are averaged over a specifiably long time, and-the thus ascertained object angle average is accepted as the new nominal directional angle of the preceding vehicle. Furthermore, a correcting angle is calculated from the difference of the nominal directional angle and the actual directional angle. The registered object angles are corrected with this difference angle.
European Published Patent Application No. 0 782 008 describes a device for calculating and correcting the deviation of the center axis of an obstacle recognition device on a vehicle and equipment for proximity-controlled cruise control based on a preceding vehicle. This system recognizes standing objects, and from the positional displacement of the standing object relative to the sensor in time, it calculates whether the standing object has a relative speed component which is orthogonal to the axis of symmetry of the sensor""s viewing zone, also called the optical axis. In the case of an accurately adjusted sensor, a mean value generation in time of this lateral relative speed gives a value tending to zero. In the case of a sensor""s viewing zone that is out of alignment, a value not equal to zero is obtained by the mean value generation in time, which, by its magnitude permits drawing a conclusion on the misalignment angle of the sensor. Using this method, a misalignment of the sensor can be recognized, and the sensor""s misalignment can be corrected.
Both methods have a device and a method, respectively, for recognizing misalignment, and both methods correct, upon recognizing misalignment, in such a way that a correcting angle ascertained from the measured values is added to the measured object angle. The axis of symmetry of the sensor is tilted by calculation in such a way that it approximately coincides with the central axis of the vehicle.
It is common to conventional methods and devices for recognizing misalignment of distance sensors that in specified travel situations they yield good results, and in other travel situations they yield results the errors of which cannot be neglected. Thus, advantageous and disadvantageous travel states exist for each system.
It is an object of the present invention to let two or more differently defined individual procedures for misalignment recognition proceed simultaneously in combination and monitor the travel state or operate a device which makes use of two or more individual procedures. These two individual procedures are developed in such a way that at least one procedure yields reliable values in each travel state. Thereby, the weakness of one procedure, namely that it yields unreliable values in this travel state, is compensated for by the strength of another method, since the latter yields reliable values in this travel state. For the evaluation of the results of the individual procedures, a quality factor is developed from the currently present travel state for each individual procedure, which are used for the weighting of the results of the individual procedures. A linked misalignment value may be determined, depending on the weighted results of the individual procedures, as well as the results of the value linkage, which is corrected as a function of these values, or as a result of which the system is switched off for safety reasons. Defects in the sensor hardware become apparent from error images which may be represented by special misalignment vectors. Such a misalignment vector is made up of a linear combination of the misalignment values of the individual procedures. By monitoring the up-to-date-misalignment vectors, some hardware functions of the sensor important to the operation may thus be monitored. The present invention is suitable for horizontal and also for vertical misalignment recognition and/or misalignment correction. In case a vertical misalignment recognition and/or correction is to be performed, the sensor may also be in a position to measure the elevation angle of reflecting objects.
If a travel situation occurs in which an individual procedure used yields unreliable measured values, the results of this procedure are weighted more lightly at this point in time than another individual procedure which is expected to yield more reliable values in this travel situation, with the aid of a quality factor. By such a combination of individual procedures, it is possible to compensate for the weak points of one procedure by the strength of another procedure. It is also possible to predict with greater probability, from a measured sensor misalignment, that there is misalignment. If both procedures determine that there is misalignment, but in different angular directions, this may be caused by too large single procedure errors. If misalignment values appear in the same angular direction and at approximately equal angles from the vehicle""s center axis, one may assume with greater probability than when only one individual procedure is used, that the sensor""s axis has been shifted. In this case, one may make a reliable correction or switch off the system at smaller misalignment values than is possible using a individual procedure. In accordance with the present invention, operation of a proximity-controlled vehicle under cruise control is much safer than operating a vehicle having a sensor which is monitored by only one individual procedure for misalignment. Furthermore, the error due to disadvantageous surroundings is held much smaller than with an individual procedure, since at the time of measuring, the more reliable procedure is treated as more dominant because of the lower weighting of the unreliable result.